The use of optical fiber ribbons as cables for the transmission of optical signals is well known in the communications industry. In a typical optical fiber ribbon, plural optical fiber waveguides are arranged and retained adjacent to one another in a generally planar orientation and encased in a common outer jacket. Until recently, the use of ribbonized optical fiber cables had been limited to long-haul trunking installations where the superior transmission efficiency and other transmission characteristics of optical fibers, as opposed to metallic conduits, for example, justified the greater expense and difficulties presented by their manufacture and installation in the field. As the demands on communications media continue to increase, more research and development effort is being dedicated to finding practical, simple and inexpensive ways to apply optical fiber cables, including ribbonized cables, to the transmission of signals over shorter distances for the interconnection of local devices, for example.
A weak link in the application of optical fiber ribbon cables generally has been the difficulty of splicing and connecting the individual fibers in a fiber ribbon cable with those of another, similar ribbon cable or and/or with signal-transmitting or signal-receiving equipment, for example. The industry has attempted to solve this problem by developing numerous prefabricated terminal connectors of various configurations for installation on the ends of optical fiber ribbon cables. Although these terminal connectors have alleviated some of the difficulties of interfacing two fiber ribbon cables in series once the connectors are installed on the ends of two ribbon cables to be joined, for example, practical difficulties still remain with attaching such terminal connectors to the ribbon cables themselves. The problem is particularly vexing for on-site field technicians attempting to repair and maintain previously installed ribbon cables. As a result, substantial research and development resources are still being expended to find better ways of fabricating optical fiber ribbon cables and terminal connectors, and of connecting prefabricated ribbon cables to prefabricated terminal connectors. The principal objective of these efforts is to create optical fiber ribbon cables and terminal connectors that are capable of easy and precise field connectorization. An important consideration in any such effort is that the end surfaces of the individual optical fibers within an optical fiber ribbon cable must align precisely with the signal-receiving or signal-emitting apparatus with which they are to interface to obtain a low-loss connection.
At present, there are two primary prefabricated multifiber terminal connectors: (1) ATandT""s MAC(trademark) and (2) the MT(trademark) connector made by U.S. Conec. Of these two, only the MT(trademark) connector lends itself to installation in the field, albeit, not simply. When a field technician desires to install an MT(trademark) connector onto an existing fiber ribbon cable, the technician cuts the ribbon cable. The insulation jacket surrounding the ribbon cable is typically slit longitudinally to allow the insulation jacket to be peeled back. If the ribbon cable is cut too deeply at this point, the optical fibers could be damaged. After peeling back the insulation jacket, the technician is left with a fiber ribbon comprising a ribbon coating (e.g., plastic) encapsulating plural optical fibers.
Frequently, a hot blade stripper is used to strip the ribbon coating from the optical fiber. This tool heats the entire end of the ribbon and has two blades that move towards one another to cut the ribbon coating and pull the coating off the optical fibers. This step sometimes causes damage to the fibers because it is very easy to cut too deeply with the blades. Once the individual optical fibers are exposed and cleaned to remove any remaining coating residue or foreign particles, the connector must be filled with an appropriate quantity of adhesive and the individual fibers manually inserted through laterally spaced guide holes in the connector. Once this is done, the adhesive is cured to secure the fibers on the connector.
Although optical fiber ribbon cables have made the use of optical fibers in and as data conduits somewhat more ubiquitous, currently available methods of stripping and connecting (i.e., splicing) optical fiber ribbon cables are labor intensive and time consuming, require a great degree of skill and care and subject the optical fibers to potential damage due to the difficulty in stripping the protective jacket and buffer from the individual optical fibers.
Attempts have been made to alleviate the difficulty and time-intensiveness of optical fiber ribbon connectorization. One such attempt is discussed in U.S. Pat. No. 5,611,017 to Lee et al. for a Fiber Optic Ribbon Cable with Pre-installed Locations for Subsequent Connectorization. U.S. Pat. No. 5,611,017 teaches a fiber optic ribbon cable that has release elements manufactured in line with the ribbon cable. The release elements provide access points to the optical fibers contained therein to allow for simplified application of a connector in the field. A pair of adhesive tape layers is applied about the optical fibers to create a fiber optic ribbon cable. When it is desired to equip the ribbon cable with a connector, the cable is cut perpendicularly to the fiber axes near the midpoint of the access points. Once the cable is cut, the adhesive tape layers and the pieces of release element may be peeled back to expose the individual optical fibers. A connector is then installed onto the exposed optical fibers, the pieces of release element removed from the tape layers and the tape layers secured to the connector. Among the drawbacks of this technique are that it requires the inclusion of release elements in line with the ribbon cable. These release elements are described as being made of plastic or ceramic, but whatever the material from which they are fabricated, their presence may constitute irregular bulges along the length of the cable. Furthermore, the inclusion of the release elements introduces numerous stress points throughout the length of the cable that may result in damage to the individual optical fibers. Still further, because of the nature of the in-line access points, one needing to install a connector at such an access point will need to locate the midpoint of the release elements with a fair degree of accuracy for cutting of the cable.
The present invention is directed to a prefabricated optical fiber cable for subsequent connectorization to a prefabricated connector, methods of fabricating the prefabricated optical fiber cable and methods of connectorizing a prefabricated optical fiber cable to a prefabricated multifiber terminal connector.
In one embodiment, an optical fiber ribbon cable comprises a plurality of elongated laterally spaced wave-transmitting optical fibers. The lateral center-to-center spacing of the optical fibers within the ribbon cable is maintained within predetermined tolerances by the inclusion of spacer fibers between adjacent optical fibers. The optical fibers and the spacer fibers are maintained in their desired positions, and protected from damage, by an encapsulation layer. The fabrication of the optical fiber ribbon cable may be such that the lateral spacing of the optical fibers is maintained by the spacer fibers along the entirety of a length of ribbon cable. The optical fibers are for transmitting signals, while the spacer fibers exist for the purpose of establishing and maintaining the lateral spacing of the optical fibers. The widths of the optical fibers and the spacer fibers are two parameters that may be varied in order to fabricate optical fiber ribbon cables for connectorization with prefabricated multifiber terminal connectors of various designs and dimensions, of which the MT(trademark) Connector is only a single example.
The materials from which the encapsulation layer, the spacer fibers and the optical fibers are each comprised are chosen based on their relative solubilities in certain solutions. More specifically, the encapsulating layer and the spacer fibers each comprise a material that is soluble in a particular solution relative to the solubility of the optical fibers in the same solution or solutions. For example, the encapsulating layer and spacer fibers may each be soluble in one or both of a particular acid and/or acetone, while the optical fibers are made from a material that is not soluble in either acetone or the particular acid. In one version, the spacer fibers and the encapsulation layer are made from the same material as one another.
When it is desired to install a multifiber terminal connector onto the optical fiber ribbon cable, the cable may be cut generally perpendicularly to the optical fiber axes. Next, a short section of at least the encapsulation layer is leached away using an appropriate solution. If the same solution used to leach the encapsulation layer will also dissolve the spacer fibers, then the dissolution of the encapsulation layer and the spacer fibers may be performed as a single step. However, if this is not the case, then once the encapsulation layer has been dissolved in a first solution, there will remain protruding from the undissolved portion of the encapsulation layer, an array of exposed optical fibers and spacer fibers. The exposed optical fibers and spacer fibers may then be subjected to a second solution that will dissolve the spacer fibers, but not the optical fibers. In either event, once all necessary dissolution steps have been performed, there will remain a plurality of optical fibers segments protruding from the undissolved portion of the ribbon. Where the dissolved length along which the encapsulation layer and the spacer fibers is not too great, the optical fiber segments will be maintained at substantially their original spacing.
To install a multifiber terminal connector onto the end of the optical fiber ribbon cable, the optical fiber segments are inserted into corresponding fiber-receiving channels in the terminal connector and secured in place with adhesive, for example. The optical fiber ribbon cables and the terminal connectors are chosen such that the lateral center-to-center spacing of the optical fiber segments corresponds to the center-to-center spacing of the fiber-receiving channels in the terminal connector with which the ribbon cable is to be connected. In this way, the optical fiber segments may be inserted into the corresponding fiber-receiving channels simultaneously, instead of individually.
In alternatives embodiments, the spacer fibers are not included over the entire length of the optical fiber ribbon cable; instead, the ribbon cable is fabricated to include at least one xe2x80x9cconnectorization region.xe2x80x9d A connectorization region is a portion of the optical fiber ribbon cable along which the center-to-center spacing tolerances of the optical fibers are maintained by spacer fibers as generally described previously (i.e., xe2x80x9cprecisely ribbonized).xe2x80x9d By including a plurality of connectorization regions spaced at intervals along the length of an optical fiber ribbon cable, the advantages of precision ribbonizing by including spacer fibers may be generally realized without the need for including spacer fibers, and maintaining center-to-center spacing tolerances, over the entire length of optical fiber ribbon cable. In regions of the optical fiber ribbon cable other than the connectorization regions, the center-to-center spacing of the optical fibers need not be maintained with any great degree of precision; but may be xe2x80x9cimprecisely ribbonized.xe2x80x9d
In some embodiments, an optical fiber cable includes a plurality of optical fibers that are unribbonized except in designated connectorization regions. In the designated connectorization regions, the optical fibers are precisely ribbonized and maintained within center-to-center spacing tolerances as described above. In the unribbonized regions, the optical fibers may be more or less randomly arranged. In some versions of such embodiments, the unribbonized regions may be encased in a cylindrical sheathing, for example, from which they would fan out into their precisely aligned positions within a ribbonized connectorization region.
In an alternative embodiment, an optical fiber cable is fabricated in accordance with a coding system that reveals to an observer certain characteristics about the optical fiber cable; for example, the widths and heights of the optical fibers included therein, the center-to-center spacings of the optical fibers and the cross-sectional geometry of the optical fibers.
In one coded embodiment, each of the spacer fibers within a connectorization region is one of a first color and a second color and the spacer fibers are arranged in one of a prescribed plurality of color combinations in accordance with a predetermined coding system in which each of the prescribed color combinations of spacer fibers is indicative of an optical fiber cable having a unique set of characteristics. To increase the number of possible combinations in the code, alternative embodiments may be fabricated in which each of the spacer fibers within a connectorization region is one of three or more colors.
An optical fiber cable having at least one connectorization region for connectorization with a prefabricated multifiber terminal connector may be fabricated by one or more of the illustrative methods described below.
In one aspect, a method of fabricating an optical fiber cable having at least one connectorization region in which the optical fibers are precisely ribbonized may include the steps of: (i) providing a plurality of optical fibers for inclusion within the optical fiber cable, each of which optical fibers has a fiber center, a fiber height and a predetermined optical fiber width and each of which comprises a first material; (ii) predetermining the desired center-to-center spacing that adjacent optical fibers are to have when normally oriented in a substantially planar configuration in the at least one connectorization region; (iii) providing at least one spacer fiber comprised of a third material for positioning in lateral abutting relationship between first and second adjacent optical fibers within the plurality of optical fibers such that, with respect to each pair of first and second adjacent optical fibers to be spaced apart, one half the optical fiber width of the first optical fiber plus one half the optical fiber width of the second optical fiber plus the sum of the spacer fiber widths of the at least one spacer fiber to be abuttingly positioned between the first and second optical fibers is equal to the predetermined center-to-center spacing within a connectorization region; (iv) arranging and temporarily restraining, so as to prevent vertical, lateral, and longitudinal movement, the first and second optical fibers of each set of adjacent optical fibers to be spaced apart in lateral abutting relationship with at least one spacer fiber positioned therebetween such that the center-to-center spacing between the first and second optical fibers is within acceptable predetermined tolerances over some length along the at least one spacer fiber; and (v) applying an encapsulation layer comprising a second material to the restrained optical fibers and the at least one spacer fiber to form a precisely ribbonized connectorization region. The second material from which the encapsulation layer is fabricated is more soluble in a first solution than the first material from which the optical fibers are fabricated, and the third material from which the spacer fibers are fabricated is more soluble in a second solution than the first material. As previously mentioned in connection with methods of connectorization, the first, second and third materials from which the optical fibers, the encapsulation layer and the spacer fibers are respectively comprised may be such that a single, common solution will dissolve the encapsulation layer and the spacer fibers, but not the optical fibers.
An advantage of the present invention is that it provides an optical fiber cable having at least one connectorization region in which the center-to-center spacings of the optical fibers correspond to the center-to-center channel spacings of the corresponding channels in a multifiber terminal connector thereby simplifying connectorization to the terminal connector.